The fluidic coupling devices that are used in medicine and biology in association with a catheter or the like, on the one hand, and with a flexible microtube, on the other hand, are usually standardized couplings of the “Luer” type, defined by the ISO 59461 standard of 1986, or of the “Luer Lock” type, defined by the ISO 594-2 standard of 1998. Referring to FIG. 1 appended to the present description, the usual coupling devices 1 essentially comprise:                a female coupling 2 into which a catheter is intended to be pushed and which comprises a conical internal fitting surface 3 that narrows toward a female end 4 at which the catheter emerges, and        a male coupling 5 which is press fitted into the female coupling 2 via its conical external surface 6 with the same conicity as the internal surface 3 of the female coupling and which narrows toward a male end 7, leaving, in the state of maximal insertion, an axial distance d1 from the female end 4. By way of example, FIG. 1 shows the position of maximal insertion 7′ that the male end 7 can have; it therefore leaves a free space (dead volume) of which the axial depth is d1, this being minimal when the surface 7 occupies the position 7′.        
Table 1 below lists the main dimension characteristics of the coupling devices of the “Luer” type (6% conicity angle) depending on the material used, according to the aforementioned standard.
TABLE 1Dimensions (mm)DimensionalRigidSemirigidparameterDescriptionmaterialmaterialBasedminMinimum diameter of3.9253.925dimensionsthe end of the maleconical coupling(referencediameter)dmaxMaximum diameter of3.9904.027the end of the maleconical couplingDminMinimum diameter of4.2704.270the opening of thefemale conicalcouplingDmaxMaximum diameter of4.3154.315the opening of thefemale conicalcouplingEMinimum length of7.5007.500the male conicalcouplingFMinimum depth of7.5007.500the female conicalcouplingOtherL*Minimum penetration4.6654.050dimensionsM*Variance over the0.7500.750penetration of thefemale couplingN*Variance over the1.0831.700penetration of themale couplingR**maxRadius of curvature0.50.5With reference to the symbols * and ** of this table:*the dimensions L, M, N result from the base dimensions, and**or equivalent entry chamfer not having sharp angles.
A major drawback of the coupling devices defined by the aforementioned standards is that the distance d1 (typically of about 3 to 6 mm depending on the type of female coupling used) between the respective ends of the male and female couplings generates a cavity forming an intrinsic dead volume that becomes disadvantageous in various circumstances. The most frequent is when the couplings are used for circulating very small samples of liquid, of an order of magnitude comparable to or even smaller than this dead volume. By way of example, when injecting or collecting microsamples of mammalian blood, it is general practice to use a flexible conduit provided with a coupling having a diameter of about 4 mm, the space thus delimited determining a dead volume of the order of 35 μl (for a cavity with a length of 3 mm) to 70 μl (for a cavity with a length of 6 mm), which dead volume may cause the following problems in use, on account of these relatively large dimensions:                since several successive microsamples serve to fill this dead volume, this delays the passage of the first microsamples and means that a larger volume of fluid is collected, which is lost, and        since the cross section of the fluidic conduit is considerably widened on account of this dead volume, various microsamples become mixed up there with one another, which is disadvantageous if the fluid is a liquid, and if these microsamples are used subsequently, for example for the purpose of analysis. This impairs their traceability and is particularly disadvantageous when monitoring processes that develop over the course of time, for example rapid biological phenomena, during which it is of fundamental importance for each microsample to be able to retain its initial characteristics throughout the process.        
Moreover, and as is shown in Table 1 above, the standards relating to the “Luer” couplings do not define a single type of coupling, especially as regards female couplings, but several types that are mutually compatible and that have dimensions in part defined in this table (these standards do not specify, for example, the dimension of the cavity between the male and female couplings). As a result, any coupling device of the “Luer” or “Luer Lock” type minimizing this dead volume must aim for compatibility with all the various dimensions of these different types, so as not to make it too difficult for users to manage the procurement of couplings.
It is also known from document U.S. Pat. No. 4,966,588 to use, for the injection of a therapeutic liquid substance, a fluidic coupling device essentially comprising:                a male coupling press fitted into a female coupling via respective cylindrical fitting surfaces provided with shoulders, this female coupling being intended to receive a cannula forming an injection tip, and        a rigid injection needle which is inserted so as to pass through the male coupling and the female coupling and also the cannula, by piercing a sealing washer positioned between the two couplings, and which is intended to be implanted in the body to be treated.        
This coupling device with a rigid injection needle passing right through the couplings and the cannula does indeed make it possible to minimize the dead volume, but it has the following drawbacks:                the diameter of the needle is small by comparison with that of the opening of the male coupling and of the fluidic conduit, which significantly reduces the flow rate and is reflected in an increased speed of the fluid (the viscosity of the latter can then pose a problem);        this device may be effective only for a single coupling procedure, since there is nothing to suggest that subsequent couplings would have the needle pass through the same orifice of the sealing washer (there being a possibility of the latter being unintentionally displaced following removal of the needle after each injection) or that this washer would then have the same leaktightness;        this device does not comply with the aforementioned “Luer” or “Luer Lock” types; and        the needle necessarily extends beyond the sealing washer by a length that may cause problems in certain applications upstream or downstream of this needle (for example when the cannula is formed by a flexible catheter, the needle may extend beyond the end of the catheter, causing it to lose its flexibility and thereby risking possible damage to the surrounding biological tissue).        
Current developments in biomedical techniques mean that it is increasingly common to use liquid microsamples (i.e. samples each having a volume of less than 100 μl and preferably less than or equal to 30 μl, such as blood samples collected from small animals). However, the sampling lines that comprise at least one coupling device of the “Luer” or “Luer Lock” type must be able to maintain the traceability of these microsamples, allowing the microsamples to be retrieved at the output end as they were at the input end. These couplings must additionally have a leaktightness that is not significantly affected by the clamping force between the male and female couplings or damaged by a succession of several assembling and dismantling procedures.
Document DE-A1-44 03 630 discloses a complex assembly of several tubes and male and female couplings in which it is the female coupling (see FIG. 3) that is modified in order to minimize the dead volume, it being noted specifically that the male coupling is in this case screwed and not just press fitted into this female coupling.
Document U.S. Pat. No. 5,964,737 discloses, in FIG. 19 thereof, a syringe terminating in a male connector piece which is press fitted into a female connector piece but which in particular does not have any flexible tube or conduit passing through it.